Signal-processing circuit, in particular operating as a rectifier and peak detector, with active elements and differential inputs

ABSTRACT

A signal-processing circuit has a first and a second input, which receive a first and a second differential signal, a third input, which receives a common-mode signal, the first and second differential signals having an equal and substantially opposite trend with respect to the common-mode signal, and a first output supplying a first processed signal, equivalent to the first differential signal rectified with respect to the common-mode signal, and satisfying throughout its course a first relation of comparison with the common-mode signal. The processing circuit is provided with first formation means for formation of the first processed signal, which operate on the basis of the first differential signal, and second formation means for formation of the first processed signal, which operate on the basis of the second differential signal; the first and second formation means co-operate in the formation of the first processed signal.

BACKGROUND

1. Technical Field

The present invention relates to a signal-processing circuit of an analog type, in particular operating as a rectifier and peak detector, with active elements and differential inputs.

2. Description of the Related Art

Rectifier and peak-detector circuits are known which enable extraction from an analog signal (for example, a voltage signal) of information correlated to its mean amplitude or else to its peak value. In a known way, these circuits are generally based upon the use of unidirectional current-conduction means (for example, diodes) for rectifying the signal, and of charge-storage means (for example, capacitors) for detecting the peak value.

It is also common to use analog circuits of a fully-differential type, i.e., ones provided with pairs of differential inputs and outputs and in particular supplying at output a first differential signal V_(P)(t) and a second differential signal V_(M)(t), which have the same amplitude but are in phase opposition with respect to one another, and vary (in a way opposite with respect to one another) around a common-mode voltage V_(CM). The use of fully-differential structures is advantageous in so far as it enables doubling of the dynamic range of the output signals and an automatic rejection of disturbance common to the two differential inputs. For example, circuit blocks of a fully-differential type are typically associated to the outputs of accelerometric sensors, gyroscopes, or other inertial sensors, for performing preliminary processing operations of corresponding output signals.

In particular, in some applications, it is required to obtain, from the pair formed by the first differential signal V_(P)(t) and the second differential signal V_(M)(t), a second pair of signals, a first peak signal V_(pp)(t) and a second peak signal V_(pm)(t), which are respectively equal to the positive peak (with respect to the common-mode signal V_(CM)) of the first differential signal V_(P)(t) and to the negative peak (once again with respect to the common-mode signal V_(CM)) of the second differential signal V_(M)(t).

FIG. 1 shows a peak-detector circuit 1 of a known type, having a first input 2 a, a second input 2 b, and a third input 2 c, which receive, from a generic time-continuous and fully-differential analog block 3, respectively the first differential signal V_(P)(t), the second differential signal V_(M)(t), and the common-mode signal V_(CM), which has a substantially constant value. The peak-detector circuit 1 has a first output 4 a and a second output 4 b on which it supplies, respectively, the first peak signal V_(pp)(t) and the second peak signal V_(pm)(t).

In detail, the peak-detector circuit 1 comprises a first detection circuit branch 1 a and a second detection circuit branch 1 b, which are identical to one another, are completely separate and independent, are connected to the first input 2 a and to the second input 2 b, respectively, and are both connected to the third input 2 c.

Each detection circuit branch 1 a, 1 b comprises: an operational amplifier 5 a , 5 b having its non-inverting input connected to the first/second input 2 a , 2 b and its inverting input connected in feedback mode to the first/second output 4 a , 4 b ; a diode 6 a , 6 b connected between the output of the operational amplifier 5 a , 5 b and the first/second output 4 a , 4 b (in particular, the diode 6 a has its anode connected to the output of the corresponding amplifier 5 a and its cathode connected to the first output 4 a , and the diode 6 b has its cathode connected to the second output 4 b and its anode connected to the output of the corresponding amplifier 5 b ); a capacitor 8 a , 8 b , connected between the third input 2 c and the anode/cathode of the corresponding diode 6 a , 6 b ; and a current generator 9 a , 9 b connected between the first/second output 4 a , 4 b and, respectively, a reference voltage GND and a supply voltage V_(DD).

Operation of the peak-detector circuit 1 (reference may be made also to FIG. 2 in which the waveforms of corresponding electrical signals are shown) is now described with specific reference to the first detection circuit branch 1 a (but similar considerations may be applied to the second detection circuit branch 1 b).

When the first differential signal V_(P)(t) is higher than the first peak signal V_(pp)(t) present on the first output 4 a , the diode 6 a conducts, and the current at output from the amplifier 5 a charges the capacitor 8 a , causing rising of the first peak signal V_(pp)(t), which “follows” the first differential signal V_(P)(t). As soon as the first differential signal V_(P)(t) drops below the first peak signal V_(pp)(t), current conduction through the diode 6 a is interrupted, and the capacitor 8 a discharges through the current generator 9 a, which extracts a current having a very low intensity (so that the first peak signal V_(pp)(t) will decrease very slowly). The flow of current that charges the capacitor 8 a resumes as soon as the first differential signal V_(P)(t) again exceeds the value of the first peak signal V_(pp)(t), which coincides with the value of the residual voltage on the capacitor 8 a added to the common-mode voltage V_(CM).

Operation of the second detection circuit branch 1 b is similar, with the difference that the flow of current at output from the amplifier 5 b discharges the corresponding capacitor 8 b when the second differential signal V_(M)(t) is lower than the second peak signal V_(pm)(t) present on the second output 4 b, and the current supplied by the current generator 9 b charges the capacitor 8 b.

It is evident that in both of the circuit branches the first and second current generators 9 a, 9 b can be constant-current sources or else can be replaced with resistors.

The circuit described has a number of drawbacks. In the first place, a problem is represented by the high area occupation, due to the need to replicate twice one and the same peak-detector circuit. In fact, the two differential signals at input are used separately for detecting the positive peak signal and the negative peak signal. In addition, the two detection circuit branches 1 a, 1 b are separate and independent, and there consequently exists the risk of “mismatch” between component values, which can cause offsets between the first and second peak signals V_(pp)(t), V_(pm)(t). In addition, each peak-detection circuit branch 1 a, 1 b functions as a half-wave rectifier, operating on just one peak (positive or negative) of the input voltage, respectively when V_(P)(t)>V_(CM), or else when V_(M)(t)<V_(CM). As compared to a full-wave rectifier, the amplitude of the output-voltage ripple (designated by r in FIG. 2) is evidently greater as the time of discharging/charging of the capacitor 8 a, 8 b increases.

BRIEF SUMMARY

One embodiment of the present invention provides a signal-processing circuit, in particular of a rectifier and/or peak-detector type, that enables the aforesaid problems and disadvantages to be overcome, either entirely or in part.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, preferred embodiments thereof are now described, purely by way of non-limiting example and with reference to the attached plate of drawings, wherein:

FIG. 1 shows a circuit diagram of a peak-detector circuit of a known type;

FIG. 2 shows waveforms of electrical quantities at output from the circuit of FIG. 1;

FIG. 3 shows a circuit block diagram of a signal-processing circuit, in particular of a rectifier type, according to one embodiment of the present invention;

FIG. 4 shows a circuit block diagram of a signal-processing circuit, in particular of a peak-detector type, according to one embodiment of the present invention;

FIG. 5 shows waveforms of electrical quantities associated to the circuits of FIGS. 3 and 4;

FIG. 6 shows a detailed circuit diagram of the circuit of FIG. 4; and

FIG. 7 shows a simplified block diagram of an electronic device incorporating the signal-processing circuit according to one embodiment of the invention.

DETAILED DESCRIPTION

As shown in FIG. 3, an analog signal-processing circuit (in particular of a rectifier type) made according to one embodiment of the present invention and designated by 10A, has a first input, a second input and a third input 11 a-11 c connected (in a way not illustrated) to the outputs of a circuit block of a fully-differential type (similar to the analog block 3 of FIG. 1). The first and second inputs 11 a, 11 b receive, respectively, a first differential signal V_(p)(t) and a second differential signal V_(M)(t) (in particular, voltage signals), which are equal in amplitude and in phase opposition with respect to one another, and the third input 11 c receives a common-mode signal V_(CM) (which is also a voltage signal). The differential signals V_(p)(t), V_(M)(t) have an equal and opposite trend with respect to the common-mode signal V_(CM). For example (see also FIG. 5), the first and second differential signals V_(p)(t), V_(M)(t) have a sinusoidal waveform around the common-mode signal V_(CM). The signal-processing circuit 10 has also a first output 12 a and a second output 12 b, present on which are a first processed signal V_(pp)(t) and a second processed signal V_(pm)(t) (in particular, rectified signals).

The signal-processing circuit 10 further comprises four current generators 14 a -14 d, which are voltage-controlled by the first differential signal V_(p)(t) or by the second differential signal V_(M)(t), and supply at output a unidirectional current flow, the value of which is a function of the value of the first differential signal V_(p)(t) or the second differential signal V_(M)(t).

In detail, a first current generator 14 a is connected between a supply line 13, set at a supply voltage V_(dd), and the first output 12 a, and has a first control terminal and a second control terminal connected, respectively, to the first input 11 a and to the first output 12 a. The first current generator 14 a is controlled by the voltage of the first differential signal V_(p)(t) and is configured to supply at output a current, the value of which is correlated to the value of the first differential signal V_(p)(t), only in the case where the first differential signal V_(p)(t) is higher than the first processed signal V_(pp)(t) (and than the common-mode signal V_(CM)). The second current generator 14 b is also connected between the supply line 13 and the first output 12 a, and has control terminals connected to the second input 11 b and to the first output 12 a so as to be controlled by the voltage of the second differential signal V_(M)(t). In addition, the second current generator 14 b is configured to supply at output a current, the value of which is correlated to the value of the second differential signal V_(M)(t), in the case where the second differential signal V_(M)(t) is higher than the first processed signal V_(pp)(t). The third current generator 14 c is connected between a reference-voltage line 15, set at a reference voltage GND, and the second output 12 b, and has control terminals connected to the first input 11 a and to the second output 12 b. The third current generator 14 c is controlled by the voltage of the first differential signal V_(P)(t) and is configured to supply at output a current, the value of which is correlated to the value of the first differential signal V_(P)(t), in the case where the first differential signal V_(P)(t) is lower than the second processed signal V_(pm)(t) (and than the common-mode signal V_(CM)). The fourth current generator 14 d is also connected between the reference-voltage line 15 and the second output 12 b, and has control terminals connected to the second input 11 b and to the second output 12 b so as to be controlled by the voltage of the second differential signal V_(M)(t). The fourth current generator 14 d is configured to supply at output a current, the value of which is correlated to the value of the second differential signal V_(M)(t), in the case where the second differential signal V_(M)(t) is lower than the second processed signal V_(pm)(t).

The signal-processing circuit 10 further comprises a first resistor 16 and a second resistor 17, which have the same value of resistance and are connected between the third input 11 c and, respectively, the first output 12 a and the second output 12 b. In particular, the first and second current generators 14 a, 14 b are configured to supply a generator current i to the first resistor 16 (in the direction indicated by the arrows in FIG. 3), and the third and fourth current generators 14 c, 14 d are configured to extract the generator current i from the second resistor 17 (once again in the direction indicated by the arrows).

Operation of the illustrated circuit is described in what follows, with initial reference to just the pair of current generators 14 a, 14 b.

As long as the first differential signal V_(P)(t) is higher than the second differential signal V_(M)(t) (or, equivalently, is higher than the common-mode signal V_(CM)), the first current generator 14 a supplies the generator current i (proportional to the value of the first differential signal V_(P)(t)) in the direction indicated, towards the first resistor 16, and the first processed signal (in this case rectified) V_(pp)(t) follows the pattern of the first differential signal V_(P)(t). In this operating condition, the second current generator 14 b is substantially off and does not supply current.

When, instead, the value of the second differential signal V_(M)(t) exceeds that of the first differential signal V_(P)(t) (or, in a similar way when the first differential signal V_(P)(t) drops below the value of the common-mode signal V_(CM), and the second differential signal V_(M)(t) exceeds said value), the first current generator 14 a turns off, and the second current generator 14 b starts operating, and supplies in turn the generator current i (proportional to the value of the second differential signal V_(M)(t)) to the first resistor 16. In this operating condition, the first processed signal V_(pp)(t) consequently follows the pattern of the second differential signal V_(M)(t), and the first current generator 14 a is substantially off and does not supply current.

Next, the first differential signal V_(P)(t) exceeds again the value of the common-mode signal V_(CM) and switches back on the first current generator 14 a, and so on, the operation described being repeated for each half-wave of the differential input signals.

As is represented with a solid line in FIG. 5, the first resulting processed signal V_(pp)(t) is constituted by a continuous series of positive half-waves (i.e., higher than the common-mode signal V_(CM)), and hence corresponds to the first differential signal V_(P)(t) (or, in an equivalent way, to the second differential signal V_(M)(t), given the corresponding waveforms of the aforesaid signals) rectified with respect to its positive component. In fact, the rectifier circuit continuously “locks” to the positive half-sinusoids (i.e., the ones higher than the common-mode signal) alternatively of the first differential input signal and of the second differential input signal, and feeds them back onto the first output 12 a. From the first processed signal V_(pp)(t), it is hence possible (in a way known and for this reason not described in detail) to extract (for example, via an appropriate filtering) information linked to the mean amplitude of the differential input signals V_(P)(t), V_(M)(t).

Operation of the pair of current generators 14 c, 14 d, which absorb current from the second resistor 17, is altogether equivalent, the second processed signal V_(pm)(t) provided on the second output 12 b being consequently constituted by a series of negative half-sinusoids (i.e., lower than the common-mode signal V_(CM)), belonging alternatively to the first differential input signal or to the second differential input signal, and corresponding to the second differential signal V_(M)(t) (or, equivalently to the first differential signal V_(P)(t)) rectified with respect to its negative component. Also in this case, from the second processed signal V_(pm)(t) it is possible to extract information linked to the mean amplitude of the differential input signals.

FIG. 4 shows a signal-processing circuit 10B made according to a further embodiment of the invention, which implements a peak rectifier of the differential input signals.

In detail, this circuit has the same characteristics as the rectifier circuit described previously, with just one difference constituted by the presence of a detection capacitor 18, connected between the first output 12 a and the second output 12 b. In the presence of the detection capacitor 18, operating as a memory element, the signal-processing circuit 10 behaves as a peak detector, detecting both the positive peak and the negative peak of the differential input signals.

In fact, due to the presence of this capacitor, the first processed signal V_(pp)(t) (represented with a dashed line in FIG. 5, in this case a peak rectified signal) rises until it reaches the positive peak of the positive half-sinusoid of the first/second differential signals V_(P)(t), V_(M)(t), and then, instead of following the waveform of the half-sinusoid, decreases very slowly with the time constant determined basically by the capacitance of the detection capacitor 18 and the resistance of the first resistor 16. The signal rises again when the second/first differential signal V_(M)(t), V_(P)(t) becomes higher than the first processed signal V_(pp)(t). In this case, the first and second current generators 14 a, 14 b are operational only during the time interval in which the first/second differential signals V_(P)(t), V_(M)(t) are effectively higher than the first processed signal V_(pp)(t) present on the detection capacitor 18, consequently having a pulsed and non-continuous operation during the entire positive half-sinusoid.

Again, the same applies to the second processed signal V_(pm)(t), which is also a peak rectified signal (represented with a dashed line in FIG. 5), which decreases until it reaches the negative peak of the negative half-sinusoid of the first differential signal V_(P)(t) or of the second differential signal V_(M)(t), and then rises very slowly towards the voltage value of the common-mode signal V_(CM), according to the time constant determined by the capacitance of the detection capacitor 18 and the resistance of the second resistor 17 (also in this case, the third and fourth current generators 14 c, 14 d have a pulsed operation).

FIG. 6 shows the detailed diagram of the signal-processing circuit 10 (when implementing a peak detector), in which the circuit architecture of the voltage-controlled current generators 14 a-14 d is highlighted. In particular, only the circuit structure of the first current generator 14 a will be described in what follows, the structure of the other generators being altogether equivalent, except for the different connections (in any case already described with reference to FIG. 4).

In detail, the first current generator 14 a is made with an active element, in particular an amplifier with unidirectional output-current flow, and comprises a biasing stage 20, a differential input stage 21, connected to the biasing stage 20, and a current-mirror stage 22, which is connected to the output of the differential input stage 21 and defines the first output 12 a of the signal-processing circuit 10.

In detail, the biasing stage 20 comprises a biasing transistor 24, of an N-channel MOSFET type, having its gate terminal receiving a constant-voltage control signal from a biasing control circuit (not illustrated) of a value such as to maintain it in conduction, its source terminal connected to the reference-voltage line 15, and its drain terminal connected to a first internal node 25 of the circuit. A biasing current I, which is determined by the circuit configuration, flows in the biasing transistor 24.

The differential input stage 21 comprises a first differential transistor 26 a and a second differential transistor 26 b, of an N-channel MOSFET type, which have source terminals connected together and to the first internal node 25. The differential input stage 21 further comprises a first mirror transistor 27 a and a second mirror transistor 27 b, of a P-channel MOSFET type, which define a current mirror with unit gain ratio.

In greater detail, the first differential transistor 26 a has its gate terminal which is connected to the first input 11 a of the circuit and receives the first differential signal V_(p)(t), and its drain terminal which is connected to the drain terminal of the first mirror transistor 27 a and also defines a differential output 28 of the differential input stage 21. The second differential transistor 26 b has its gate terminal connected to the first output 12 a, and its drain terminal connected to the drain terminal of the second mirror transistor 27 b. The first mirror transistor 27 a also has its source terminal connected to the supply line 13 and to the source terminal of the second mirror transistor 27 b, and its gate terminal connected to the gate terminal and to the drain terminal of the same second mirror transistor 27 b (which is hence diode-connected).

The current-mirror stage 22 is configured to define a mirror ratio 1:K (K designating the mirror factor) between the current at output from the differential-input stage 21 and the generator current i supplied (in a unidirectional way) on the first output 12 a.

In detail, this stage comprises a third mirror transistor 29 a and a fourth mirror transistor 29 b, of a P-channel MOSFET type. The third mirror transistor 29 a has its drain terminal connected to the differential output 28 and to the gate terminal of the same transistor (which is hence diode-connected), its source terminal connected to the source terminal of the fourth mirror transistor 29 b and to the supply line 13, and its gate terminal connected to the gate terminal of the same fourth mirror transistor 29 b. The fourth mirror transistor 29 b moreover has its drain terminal connected to the first output 12 a and supplying the generator current i.

When the voltage of the first differential signal V_(P)(t) is higher than the first processed signal V_(pp)(t), the unbalancing of the pair of input differential transistors causes the biasing current I to circulate in the first differential transistor 26 a and to reach the differential output 28. This current is then mirrored by the current-mirror stage 22 and defines (increased by the mirror factor K) the generator current i. Instead, when the voltage of the first differential signal V_(P)(t) is lower than the first processed signal V_(pp)(t), the biasing current I circulates through the second differential transistor 26 b and does not reach the current-mirror stage 22 through the differential output 28. It follows that the first current generator 14 a does not supply a significant current on the first output 12 a.

The first current generator 14 a is hence indeed driven by the voltage of the first differential signal V_(p)(t) and enables a unidirectional current flow towards the first resistor 16 only in the case where the same differential signal is higher than the value of the first processed signal V_(pp)(t).

In particular, in small-signal regime, the generator current i can be expressed as:

i=g _(m) ·K·v _(d)

where g_(m) is the transconductance gain of the differential-input stage 21, K is the aforesaid mirror factor, and v_(d) is the differential unbalancing voltage of the pair of differential transistors 26 a, 26 b.

As previously highlighted, the structure and operation of the other current generators 14 b-14 d are substantially equivalent. It is pointed out only that the third and fourth current generators 14 c, 14 d have MOSFET transistors with opposite channel, in so far as the generator current i is in this case extracted by the second resistor 17.

From what has been described and illustrated, the advantages of the signal-processing circuit according to one embodiment of the invention are evident.

In particular, the circuit described enables detection of an (maximum and minimum) amplitude peak of voltage signals coming from an analog circuit block with differential output. In addition, this circuit can implement a full-wave rectifier (or double half-wave rectifier), by rectifying the signals at output from the analog block that precedes it with respect to their common-mode voltage. As may be appreciated from the above description, the advantage of this circuit derives from the joint use, for the formation of the processed output signal, of both differential input signals V_(p)(t) and V_(m)(t), exploiting both of the half-waves, i.e., the positive one and the negative one, of these signals. In particular, for the formation of the processed signal V_(pp)(t), V_(pm)(t), the first differential signal V_(p)(t) or the second differential signal V_(m)(t) are used alternatively, when they satisfy a desired relation of comparison with the same processed signal. At each half-wave one pair of the four current generators 14 a-14 d controlled by the voltage of the differential input signals (for example, the first current generator 14 a and the third current generator 14 c) is in conduction, and at the subsequent half-wave the other pair of the same generators (in the example, the second current generator 14 b and the fourth current generator 14 d) is in conduction, so that both the positive rectified signal and the negative rectified signal are supplied at output. The difference thus emerges clearly with respect to traditional rectifier/peak-detector circuits, in which only one input signal is used for processing (in the case of differential signals, only the first differential signal V_(P)(t) or the second differential signal V_(m)(t)).

The circuit advantageously acts as a full-wave rectifier. Consequently, given the same component values (in particular of the resistors and of the capacitor), it is possible to have a ripple on the voltages of the first and second processed signals V_(pp)(t), V_(pm)(t) that is reduced as compared to traditional circuits (for example, of the type illustrated in FIG. 1); or else, given the same ripple amplitude, it is possible to use passive components having a lower value.

In addition, the signal-processing circuit 10 is a single integrated circuit that can be made in a single die of semiconductor material. This characteristic, in addition to leading to a reduction of area occupation with respect to traditional solutions, improves matching between the components and the signal paths. In particular, the various transistors implementing the controlled current generators are formed in a interdigited configuration within the die, and are consequently effectively closely matched.

Moreover, it is straightforward to vary the mirror factor K of the current-mirror stage 22 of the current generators 14 a-14 d on the basis of the dynamic performance required of the circuit and of the load to be driven.

As shown schematically in FIG. 7, the signal-processing circuit 10 can advantageously be used in an electronic device 30, which incorporates a MEMS sensor 32 (for example an accelerometer, a gyroscope, or a magnetometer). The MEMS sensor 32 comprises a detection structure of a microelectromechanical type (provided in a known way with at least one mobile mass free to move with external stresses), and is associated to a fully-differential analog block 34 for performing a first conditioning of the detected signals. The signal-processing circuit 10 is connected to the output of the fully-differential analog block 34 for detecting information correlated to the amplitude (for example, to the peak amplitude) of the signals detected and processed. For example, in a known way, the presence of a peak detector is advantageous in the actuation loop of a MEMS gyroscope, since for the control of the gyroscope it is helpful to know the maximum amplitude of the velocity oscillations of the mobile mass of the detection structure.

There is a wide range of electronic systems 35 in which the electronic device 30 can find advantageous application: for example, GPS systems, in which with the aid of MEMS sensors (such as gyroscopes, accelerometers, etc.) it is possible to trace the position of a person even when the satellite link is not usable; automotive systems, in which accelerometers and gyroscopes supply aid-to-drive information; video-acquisition systems (for example cameras or camcorders) in which gyroscopes can be used for correcting trembling of the user's hand when the resolution exceeds a given level (for example, 4-5 Mpix). The above systems typically comprise a control unit 36 (for example, a microprocessor control unit), supervising their operation; the control unit 36 is connected to the electronic device 30, and acquires the aforesaid amplitude information from the signal-processing circuit 10.

Finally, it is clear that modifications and variations can be made to what is described and illustrated herein without thereby departing from the scope of the present invention, as defined in the annexed claims.

In particular, the circuit may comprise only a pair of current generators and just one resistor (in particular, the first and second current generators 14 a-14 b and the first resistor 16, or else the third and fourth current generators 14 c-14 d and the second resistor 17), in the case where it is desired to obtain at output only a rectified signal (or peak rectified signal), that is positive or negative with respect to the common-mode signal V_(CM).

In addition, there could be advantageously envisaged the presence of two controlled switches between the first output 12 a and the second output 12 b, and a respective terminal of the detection capacitor 18 so as to connect or disconnect the detection capacitor 18 to/from the circuit and thus selectively implement the function of rectifier or of peak detector.

The first and second differential signals V_(P), V_(M) could have a waveform different from the sinusoidal waveform described, albeit having opposite variations (i.e., being in phase opposition) with respect to the common-mode signal V_(CM).

Finally, the aforesaid first and second differential signals, with the highlighted features, could even not come from a fully-differential analog block, but be generated in any other way in itself known.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A signal-processing circuit, comprising: first and second inputs designed to receive first and second differential signals, respectively; a third input designed to receive a common-mode signal, said first and second differential signals having substantially opposite trend with respect to said common-mode signal; a first output designed to supply a first processed signal, equivalent to said first differential signal rectified with respect to said common-mode signal and satisfying a first relation of comparison with said common-mode signal; first formation means for forming said first processed signal, which are configured to operate based on said first differential signal; and second formation means for forming said first processed signal, which are configured to operate based on said second differential signal, said first and second formation means being configured to co-operate in forming said first processed signal.
 2. The circuit according to claim 1, wherein said first and second formation means are configured to operate in a substantially mutually exclusive way, respectively when said first differential signal and said second differential signals satisfy said first relation of comparison with said first processed signal.
 3. The circuit according to claim 1, wherein said first and second formation means comprise respective resistors and respective controlled current generators, controlled, respectively, by said first and second differential signals, and configured to supply said resistor with a unidirectional generator current the value of which is a function, respectively, of said first differential signal and of said second differential signal.
 4. The circuit according to claim 1, wherein: said first and second differential signals are voltage signals; said first formation means comprise a first resistor connected between said first output and said third input, and first controlled current generator connected to said first output, the first current generator being voltage-controlled by said first differential signal; said second formation means comprise said first resistor and second controlled current generator connected to said first output and voltage-controlled by said second differential signal.
 5. The circuit according to claim 4, wherein: said first controlled current generator has a first and a second control terminal connected, respectively, to said first input and to said first output; said second controlled current generator has respective first and second control terminals connected, respectively, to said second input and to said first output; said first controlled current generator supplies current to said first resistor when said first differential signal satisfies said first relation of comparison with said first processed signal; and said second controlled current generator supplies current to said first resistor when said second differential signal satisfies said first relation of comparison with said first processed signal.
 6. The circuit according to claim 1, wherein said first processed signal is a full-wave rectified signal.
 7. The circuit according to claim 1, wherein: said first processed signal is a peak rectified signal; and said first and second formation means further comprise a capacitor connected to said first output.
 8. The circuit according to claim 1, further comprising: a second output designed to supply a second processed signal, equivalent to said first differential signal rectified with respect to said common-mode signal and satisfying a second relation of comparison with said common-mode signal; third formation means for forming said second processed signal, which are designed to operate based on said second differential signal; and fourth formation means for forming said second processed signal, which are designed to operate based on said first differential signal, said third and fourth formation means being configured to co-operate in the formation of said second processed signal.
 9. The circuit according to claim 8, wherein: said third and fourth formation means are configured to operate in a substantially mutually exclusive way, respectively when said second differential signal and said first differential signal satisfy said second relation of comparison with said second processed signal; and said first and said third formation means are configured to operate substantially simultaneously in a first operating interval, and said second and said fourth formation means are configured to operate substantially simultaneously in a second operating interval, substantially distinct from said first operating interval.
 10. The circuit according to claim 8, wherein said first and second differential signals are voltage signals; said third formation means comprise a second resistor connected between said second output and said third input, and third controlled current generator connected to said second output and voltage-controlled by said second differential signal; and said fourth formation means comprise said second resistor and fourth controlled current generator connected to said second output and voltage-controlled by said first differential signal.
 11. The circuit according to claim 10, wherein: said third current generator have respective first and second control terminals connected, respectively, to said second input and to said second output; and said fourth current generator have respective first and second control terminals connected, respectively, to said first input and to said second output.
 12. The circuit according to claim 8, wherein said first, second, third and fourth formation means are arranged in one and the same integrated circuit within one and the same die of semiconductor material, in such a manner that corresponding electrical characteristics are closely matched.
 13. The circuit according to claim 1, wherein each of said first and second formation means comprises respective controlled current-generators provided with an amplifier with unidirectional current flow controlled by a respective one of said first and second differential signals.
 14. The circuit according to claim 13, wherein said respective current-generators comprise: a differential input stage, which is configured to receive at input said respective one of said first and second differential signals and said first processed signal and supplies at output a differential current correlated to a difference between said respective one of said first and second differential signals and said first processed signal; and a current-mirror stage connected at input to said differential input stage and at output to said first output and configured to mirror said differential current on said output with a mirror factor, generating said generator current in a unidirectional way.
 15. The circuit according to claim 14, wherein said respective current-generators further comprise a biasing stage connected to said differential input stage and configured to supply to said differential input stage a biasing current that is a function of said respective one of said first and second differential signals.
 16. The circuit according to claim 15, wherein said differential input stage comprises: a first differential transistor and a second differential transistor, which are connected to said biasing stage and have respective control terminals, which receive, respectively, said respective one of said first and second differential signals and said first processed signal; and a first mirror transistor and a second mirror transistor connected between a reference-voltage line and, respectively, said first differential transistor and said second differential transistor, said first and second mirror transistors forming a current mirror supplying said differential current to said current-mirror stage.
 17. An electronic device, comprising: a signal-processing circuit, the signal processing circuit including: first and second inputs designed to receive a first and a second differential signal; a third input designed to receive a common-mode signal, said first and second differential signals having substantially opposite trend with respect to said common-mode signal; a first output designed to supply a first processed signal, equivalent to said first differential signal rectified with respect to said common-mode signal and satisfying a first relation of comparison with said common-mode signal; first formation means for forming said first processed signal, which are configured to operate based on said first differential signal; and second formation means for forming said first processed signal, which are configured to operate based on said second differential signal, said first and second formation means being configured to co-operate in forming said first processed signal.
 18. The device according to claim 17, comprising: a detection structure of a microelectromechanical type configured to generate electrical quantities as a function of a quantity to be detected; and a differential processing block connected to said detection structure and configured to generate, as a function of said detected electrical quantities, said first and second differential signals and said common-mode signal for said signal-processing circuit.
 19. The device according to claim 18, wherein said detection structure includes an inertial sensor.
 20. A signal-processing method, comprising: acquiring first and second differential signals and a common-mode signal, said first and second differential signals having a substantially opposite trend with respect to said common-mode signal; and forming a first processed signal jointly based on said first differential signal and said second differential signal, the first processed signal being equivalent to said first differential signal rectified with respect to said common-mode signal and satisfying a first relation of comparison with said common-mode signal.
 21. The method according to claim 20, wherein said step of forming a first processed signal comprises: forming said first processed signal based on said first differential signal when said first differential signal satisfies said first relation of comparison with said first processed signal; and forming said first processed signal based on said second differential signal when said second differential signal satisfies said first relation of comparison with said first processed signal.
 22. The method according to claim 20, further comprising: forming a second processed signal, equivalent to said first differential signal rectified with respect to said common-mode signal and satisfying a second relation of comparison with said common-mode signal, said step of forming a second processed signal including: forming said second processed signal based on said first differential signal when said first differential signal satisfies said second relation of comparison with said second processed signal; and forming said second processed signal based on said second differential signal when said second differential signal satisfies said second relation of comparison with said second processed signal.
 23. The method according to claim 20, wherein forming a first processed signal comprises supplying to a resistor a generator current with unidirectional flow, the value of which is a function of said first differential signal in a first operating condition and a function of said second differential signal in a second operating condition.
 24. The method according to claim 23, wherein said first operating condition corresponds to a condition in which said first differential signal satisfies said first relation of comparison with said first processed signal, and said second operating condition corresponds to a condition in which said second differential signal satisfies said first relation of comparison with said first processed signal.
 25. A method comprising: receiving a first input signal and a second input signal in phase opposition to the first input signal; generating a first current through a first resistor connected to a first output node while a voltage of the first input signal is greater than a first output voltage on the first output node; and generating a second current through the first resistor while a voltage of the second input signal is greater than the first output voltage.
 26. The method of claim 25 wherein a second resistor is connected between the first resistor and a second output node, the first and second resistors being in series with each other.
 27. The method of claim 26 wherein the capacitor is connected between the first and second output nodes.
 28. The method of claim 27 wherein a common mode node between the first and second resistors is held at a common mode voltage level.
 29. The method of claim 28 comprising: allowing the first and second currents to flow through the second resistor while either the first or second input voltage is lower than a second output voltage on the second output node; and maintaining the second output voltage at a level representative of a second peak of the first and second voltage opposite to the first peak of the first and second voltage by storing charge on the capacitor.
 30. The method of claim 29 wherein the first and second resistors are equal to each other.
 31. The method of claim 29 wherein the first and second currents are equal to each other.
 32. The method of claim 25 comprising maintaining the first output voltage at a level representative of a first peak of the first and second voltage by storing charge on a capacitor coupled to the first output node. 